The purely mechanical control devices used for internal combustion engines as for instance interrupting mechanisms for the ignition, mechanical triggers for direct fuel injection etc. have often proved too erratic and insufficiently adaptable for achieving optimum results. Non-mechanical, electronically operated regulating units require extremely precise reference signals which correspond to given operational states of the internal combustion engine and with whose help the internal combustion engine and the electronic regulating unit are synchronized. Any lack of precision in the reference signals annuls the advantages of a more exact regulation, which could result from the use of an electronic regulating unit.
The derivation of a reference signal for the ignition of an internal combustion engine from an impulse generator is known from German AS 25 04 843. This impulse generator scans by means of a sensor the markings placed on an engine component, e.g. a flywheel, rotating synchronously with the crankshaft. If the approach is applied to a four cycle internal combustion engine, then the number of markings is one half as large as the number of the cylinders. Indeed, as each cylinder fires only at every second revolution of the crankshaft, each indicator signal is used for two cylinders. Such an arrangement, however, creates difficulties in the case of internal combustion engines with an odd number of cylinders since the intervals between ignitions do not correspond to 180.degree. turns of the crankshaft, i.e. not all indicator signals may be allowed to produce reference signals which for instance would signal the beginnings of the work-cycles of a piston-cylinder unit.